1. Field of the Invention
The present invention relates to an antenna for use in mobile communications such as automobile telephones and MCA (multi-channel access), etc. which is flat-plate shaped and installed in a flat portion such as roof, trunk lid, etc. of the body of a vehicle such as an automobile, etc.
2. Prior Art
Various types of wire-form or linear antennas have been used in the past as antennas for mobile communications. The reasons for this are that wire-form antennas have maximum radiative characteristics in the horizontal direction, as required for mobile communications, and such antennas can easily be endowed with characteristics which are non-directional in the horizontal plane. Furthermore, antennas used for automobile telephones and MCA require broad-band characteristics, and since broad-band techniques have been well established for wire-form antennas, the design and development of such antennas are relatively easy.
In recent years, flat-plate antennas have received attention as antennas for use in mobile communications. The reason for this is that when a flat-plate antenna is attached to an automobile, there is no projecting object as in the case of conventional and antennas, and there is no deleterious effect on the style of the automobile, and wind noise occurring during operation of the automobile is decreased. Furthermore, since there is no danger that the antenna will contact car-wash machinery, garages or roadside trees, etc., the problem of damage to the antenna from such sources is eliminated. In these and other respects, such antennas have great practical merit.
In flat-plate antennas it is necessary to endow the antenna with broad-band characteristics. For this reason, antennas with a multi-layer structure have been proposed in the past. Such multi-layer antennas, however, has a complex integral structure and is therefore difficult to adapt as a commercial product.